Mixed-salt lubricants



Uited rates Patent @filice Patented Jan. 1, 1963 3,671,547 ldlXEL SALTLUBRE CANTS Arnold .l'. MOBWaY, (Iiarlr, Ni, assiguor to Esso Researchand Engineering l-Tompuny, a corporation of Delaware No Drawing. FiledAug. 23, 1960, SEE. No. 51,255 Claims. (Cl. 252-439) This inventionrelates to fluid and semi-fluid lubricating oil compositions having goodextreme pressure and 'antiwear properties. Farticularly, the inventionrelates to a lubricant comprising lubricating oil containing ananhydrous mixture of metal salts of low molecular weight carboxylic acidand moderate molecular weight carboxylic acid, which compositions areuseful for the lubrication of the upper cylinders of marine dieselengines.

This application is a continuation-in-part of U.S. patent applicationSerial Number 498,740, by Arnold J. Morway, filed April 1, 1955, and nowabandoned.

Marine diesel engines have become widespread in their use. in theseengines there has always been a serious Wear problem with regard to thepiston, the piston rings and the surface of the cylinder liner. Thisproblem of wear has been aggravated by the recent growing tendency touse low cost residual type fuel oils. These residual fuel oils contain 2to 4 wt. percent sulfur, as compared to distillate oils which generallyhead under 1.5% sulfur. However, these residual fuels represent a largeeconomic saving over the previously used distillate fuel oils.Unfortunately, because of their high sulfur content, the residual fuelsresult in increasing the liner and cylinder wear from 56 to 500% overthe wear previously encountered with distillate fuels. This increasedWear is primarily due to acids formed by the combustion of the sulfur,which acids corrode the steel surfaces of the engine.

in lubricating these ciesel engines, a fluid or semi fluid lubricant issprayed directly onto the cylinder upon each stroke of the piston bymeans of a centralized forcefeed lubrication system. The lubricant is toa large extent consumed during each stroke of the piston, therebyrequiring continuous application of the lubricant.

In order to be suitable for such lubrication use, it has been determinedthat the lubricant should have a fluid or semifluid consistency. This isdesired in order that the lubricant may be readily pumped through theaforementioned forced lubrication systems normally associated Withmarine diesel engines and will spread or wet the piston sufficientlyduring each stroke to achieve an overall coating on the piston surface.It has been further found that extreme pressure ch racteristics arenecessary, since the pressure of the piston rings against the cylinderliner is very considerable. Thus, such lubricants should be able tocarry at least 6 weights in the standard Almen extreme pressure testunder gradual loading. A third requirement of such lubricants is thatthey have good antiwear properties. Because of the giant size of thepistons and cylinders used in such engines (e.g. piston and cylinderdiameters of 36 to 60 inches are common), wear is a serious problem.Once the cylinder linear has worn more than about 0.6% of its diameter,it is necessary that it be replaced. In a typical marine engine of 8 to16 cylinders such replacement cost may run in the order of severalthousand dollars per cylinder. Wear of the piston and rings are also anexpensive problem. It is, therefore, essential that their wear beminimized and for this purpose lubricants to be acceptable should haveWear scar diameters of 0.19 to 0.28 mm. as measured in the Shell 4 ballwear test under relatively severe conditions of load versus times, i.e.under a 10 kilogram load, at 1809 rpm. for 1 hour at 77 F. The fourthmajor requirement of a lubricant of this type is that it should be ableto minimize the wear due to corrosiveness caused by the degradationproducts of the oil and particularly of the sulfur. A fifth importantrequirement is that the lubricant be storage stable, even when subjectto long periods of vibration as occurs during storage in a ships engineroom and in the presence of minor amounts of moisture.

It has been found that requirements for the above type of lubricant canbe obtained by thickening oil with 5 to 12, preferably 6 to 8 wt.percent of total thickener comprising calcium salt of acetic acid or itsanhydride in combination with calcium salt of C to C fatty acids in amolar equivalent ratio of about 11.5:1 to 2521 of said acetic acid oranhydride per mole of said higher fatty acid. At molar ratios of lessthan 11.5:l it has been found that insufiicient extreme pressure andantiwear properties are obtained and that the lubricant requires alarger amount of salt per amount of oil as well as havlog a viscositythat is excessive for pumping and spraying onto the piston. At molarratios greater than 25:1, it has been found that the lubricant isunsuitable because of storage instability since the salts will settleout of the oil leading to clogging of the lubrication system and thelubricant tends to become more susceptible to water solubility, i.e.poor sight glass performance.

The intermediate molecular Weight acids used in preparing the thickenerare those aliphatic straight chain monocarboxylic acids containing fromabout 7 to 10 carbon atoms. Either saturated or unsaturated fatty acidsmay be utilized, though the saturated fatty acids are preferred. Thecorresponding branched chain acids are not suitable since they result inunstable lubricants in which the salts readily separate from the oil.lntermediate molecular weight straight chain monocarboxylic acids comingwithin the above prescriptions are exemplified by heptanoic (enanthic),octanoic (caprylic), nouanoic (pelargonic) and decanoic (capric).Commercial mixtures of these intermediate molecular Weight carboxylicacids having an average saponification of from about 310 to 440,preferably 320 to 420 can also be employed.

The metal component of the mixed salt composition is preferably calciumsince it results in the production of stable lubricants having excellentload carrying and antiwear characteristics even without the use ofconventional extreme pressure and stabilizing agents. The other alkalineearth metals such as barium, strontium and magnesium are inferior tocalcium in these respects as are the alkali metals, e.g. sodium,potassium and lithium.

The anhydrous mixture of calcium salts of the invention may be preparedby coneutralization of a mixture of the acids with suitable bases,particularly the hydroxides and/or carbonates of calcium. Theconeutralization step may be carried out in situ in the oil menstruum towhich the mixture of salts is to be applied in actual use. The maximumtemperature at which coneutralization is carried out or the temperatureto which the coneutralized material is heated will generally be in therange of about 250 to about 350 F. The salt mixture should be heateduntil anhydrous, i.e. there is no free or unbound water present. If theacids are coneutralized then it is generally desirable to use a slightexcess of base, e.g. lime, in order thickener.

u to form a slightly alakaline final product, e.g. 0.05 to 0.2 wt.percent alkalinity as measured in terms of NaOH. This alkalinity acts toneutralize corrosive acids formed by degradation of the lubricant duringuse and also imparts conditions of greater stability.

If the acids are to be coneutralized with commercial lime, it has beenfound that sedimentation can be reduced by first partially neutralizingthe acids with lime,

cooking for about 2 to 4 hours, below 225 F., then adding the remainderof the lime to complete the neutralization and in fact, form a slightlyalkaline product. By this method, the CaCO which is present incommercial lime in quantities up to 5 wt. percent will be forced tosubstantially complete reaction with the acids. Otherwise, the calciumhydroxide will react preferentially to the calcium carbonate so that thedesired excess alkalinity will be primarily due to the calciumcarbonate. Unfortunately, the unreacted calcium carbonate tends tosettle out and results in sedimentation of the final product.

However, the coneutralization methods outlined above are not necessaryas long as the two classes of salts are present when the composition isheated to dehydration temperatures within the range of 250 F. to 350 F.Thus, the mixture of calcium salts of the invention may also be preparedby separately preforming in aqueous media at least a portion or all ofthe low molecular weight acetate salt and/or the intermediate molecularweight carboxylic acid salt and heating them together undersubstantially dehydration conditions. The salts may also be intimatelymixed prior to the heating step.

The use of preformed metal salts may also be desirable for otherconsiderations. The production of the mixtures of calcium salts hereinvolved requires large amounts of low molecular weight carboxylicacids, particularly, acetic acid or its anhydride. These acids may bepurchased in carload or tank car lots; but they require tankage withpiping to the kettles and special handling precautions to prevent themfrom solidifying in the piping and from corroding the tanks and pipes.By supplying a portion or all of the required low molecular weight acidin the form of preformed metal salt, for example, calcium acetate, thedrawbacks just mentioned may be minimized or eliminated. Theseadvantages may be obtained by replacing about 30 to 80%, preferably, atleast about 50%, of the free acid and its stoichiometric equivaa lent offree base with the preformed metal salt.

In general, the lubricating oil should have a viscosity Within the rangeof about 100 to 2,500 SUS at 100 F. and about 35 to 200 SUS at 210 F., apour point of about +20 to 75 F., and a flash point of about 350 to 650F. A viscosity index of 100 or higher is also desirable, though mineraloils having a lower viscosity index can be desirably employed. Thelubricating oil base can also consist of a blend of about 50-85 wt.percent of a relatively low viscosity oil of 30 to 70 SUS at 210 F., andabout -50 wt. percent of a relatively high viscosity oil of 200 to 2,500SUS at 100 F. Mineral oil mixtures of to 50 wt. percent naphthenic oilof V.I. of to 60 and viscosity of 50 to 80 SUS at 210 F. with 80 to 50wt. percent of solvent extract oil of VI. of 0 to -100 and viscosity of100 to 175 SUS at 210 F. have been found very desirable in preventingfouling of sight glasses which are normally used in marine dieselforcedfeed systems. The solvent extract oil used in this type offormulation can be prepared by solvent extraction of paraffinic or mixedbase lubricating oil with phenol, furfural, nitrobenzene, etc. as iswell known in the art.

Synthetic non-hydrocarbon oils, such as silicone oils do not give thesame results as mineral oils because of their high wear impartingproperties which are modified but not sufficiently overcome by thecalcium mixed-salt Furthermore, synthetic oils such as polysilicones areunduly expensive since the lubricant is continuously consumed during usein marine diesel engines, rather than being recirculated.

Various additives can be added to the finished lubricant in amounts of0.1 to 10.0 wt. percent, based on the weight of the finished lubricant.Among additives that can be added are corrosion inhibitors such assodium nitrite, lanolin, wool grease stearine; antioxidants such asphenyl a-naphthylamine; auxiliary extreme pressure agents; dyes; etc.The temperature at which the mixture of calcium salts is prepared orheated is an important feature of the present invention, since itdetermines in a large measure the physical as well as the chemicalcharacteristics of the resulting products.

In accordance with this invention maximum dehydration temperatures ofabout 250 to 350 F., preferably, about 300 to 320 F., are employed toprepare the anhydrous (i.e. dry) mixtures of salts. At either lower orhigher temperature the nature of the reaction products differssignificantly from the products obtained at the preferred dehydrationtemperature with regard to such properties as appearance, stabilty, etc.Heating to high temperatures, e.g. about 400 to 550 F. will result ininstability or undue thickening of the lubricant per given amount ofsalt, while heating at temperatures below 250 F. does not completelyeliminate free water, which has a tendency to form solid (hydrous)products which are most undesirable.

The finished lubricant will comprise a major amount of lubricating oiland about 5 to 12, preferably 6 to 8 wt. percent of the mixed saltcombination. For economy purposes in heating during large scalemanufacture, concentrates of 35 to 50 wt. percent of the mixed salts inoil can be made by the in .situ preparation technique and then theconcentrate is diluted with additional oil to form the finishedlubricant. This dilution is readily made by adding the additional oiland mixing in the kettle or by using a pump around system where thelubricant is passed from the kettle to a pump and then back to thekettle until completely mixed. Both the concentrate and finishedlubricant can be homogenized in a Morehouse mill, Charlotte mill, Gaulinhomogenizer, etc.

EXAMPLE I (All parts by Weight) A grease was prepared by charging 88.72parts of mineral lubricating oil having a viscosity of 70 SUS at 210 F.and 4.13 parts of hydrated lime to a steam heated kettle and slurriedtogether to form a smooth uniform slurry. Steam was then passed into thekettle jacket, and the ingredients warmed to P. Then 5.63 parts ofglacial acetic acid and 1.34 parts of caprylic acid (commercialgrade-Saponification No. 327 mg. KOH per gm.) was added and thetemperature was raised to about 300 F. and maintained at thistemperature for about 3 hours. The mixture was then cooled to 200 P.where 0.18 part of phenyl alphanaphthylamine was added as anantioxidant. The mixture was further cooled to room temperature whilestirring continuously. The resulting lubricant composition was thenhomogenized by passage through a Gaulin homogenizer operating at 5000p.s.i. This product contained calcium salt of acetic acid to calciumsalt of caprylic acid in a molar ratio of 12 to 1 and was employed as amarine diesel engine upper cylinder lubricant where it effectivelyreduced cylinder liner wear and minimized acid corrosion.

The above product was tested in a total of seven ships being used in theNo. 4 cylinder of each marine diesel engine, while for comparisonpurposes the No. 1 cylinder of each of said engines was lubricated witha conventional straight mineral oil marketed as a marine diesel cylinderlubricant. All cylinder liners were new at the start of the test. Thefollowing table summarizes the result obtained, listing the enginestested, the type fuel that they operated upon, the length of the testand the average cylinder wear obtained in terms of inches/ 1000 hoursoperation together with the wear reduction.

Table l COMPARATIVE SERVICE PERFORMANCE Test ship service. Tanker TankerPassenger Passenger Tanker Tanker Tanker Test ship number 1 2 3 4 5 6 7Engine 2 Burm. & 2 Burrn. dz 2 Doxford, 6- 2 Fiat, -cyl., Harland 8:Sun-DOXiord, S O 'OTd,

Wain, S-cyL, Wmn,-9 cyl., cvl., 2-stroke, 2stroke, Wolfi, 6-cyl.,5-cyl., 2- 5-cyl., 2 strolrc, 2-stroke, single-acting. single-acting.4-stroke, stroke, singlestroke, singlesingie-acting. single-acting.single-acting. acting. acting. /stroke 740/l,400 1pm-.-- HO/1,400 mmSTU/2,320 mm"..- 750/1,320 mm 740/1,500 mm 813/2410 mm 81.312410 mm-Broke ilOfSOpOVi 7,000 at 118 7,100 at 112 6,300 at 105 7,750 at 1203,300 at 110 7,500 at 94 7,500 at 94 Fwy rpm. r.p.1n. r.p.m. r.p.m.r.p.rn. r.p.m. r.p.m.

Sulfur, Weight 3.3-4 2 2.2-3.3 3.0-- 2.2-? 5 31-4.. 1.2-2.3 1.2-2.3....

pei'cen t. VISFisI UEQBFSSU '1,8002,700.. 750-1,500 700 450-1,0000001,100 4004,000 4904,0011.

a- Test HOLES..- 2,5005,600 5,000 5001,500 3,000 2,000 10,000 5,400.Avg. cyl. wear inches/1,000 hrs.:

Prior C0m- 0.019 0.021. 0.025 0.016 0.008 0.020- 0.020.

mercial lubricant. Lubricant 01 0.013 0.004 0.006 0.002 No measurable0.008 0.010-

I. 1tlvear in 2,000

r. Wear rcduc- 30... 84"-.. 74 00 60 50.

tion, percent.

In the table, Tanker 1 had two Burmeister and Wain Table II engines,each having a bore of 740 mm., a stroke of 1400 and developing 7000brake horsepower. Both engines were operated on high sulfur contentresidual fuel oil. One engine was tested for 2500 hours and the otherfor 5600 hours. The average liner wear of the No. 1 cylinder of the twoengines using a commercial straight mineral oil marine diesel lubricanwas 0.019 inch per 1000 hours operation. The average liner wear of theNo. 4 cylinder of the two engines, using the lubricant of Example I, was0.013 inch per 1000 hours operation. The composition of the inventionthus gave less wear than the commercial oil, which was one of the bestavailable for marine diesel use. Even better results were obtained inthe other ships under test.

Usually when cylinder liner wear exceeds a total of 0.6% of the bore ofthe cylinder, it is necessary to replace the cylinder liner. Thus, foran engine of 700 mm. bore, the cylinder liner would generally be removedafter Wear of 4.2 mm. or about 0.12 inch. For an average ship having twoengines of 8 cylinders each or a total of 16 cylinders, this replacementcost will be about $40,000 to $60,000 plus the cost of the downtime ofthe ship. It is thu seen that the percent wear reduction shown in thepreceding table represents a very substantial economic saving.

EXAMPLE II A series of lubricants (A to E) was prepared to demonstratethe criticaliiy of the mol ratio of the acetate to salt of the higherfatty acid. These lubricants were prepared as follows: About 99% of thehydrated lime was dispersed in about a sixth of the mineral oil. Thenglacial acetic acid was slowly added to the lime-oil dispersion and nextthe capric acid was added. The mixture was continuously mixed while bothacids were added and the temperature maintained below 200 F. Theremaining 1% lime was added to complete the neutralization of the acids.External heating was next applied and the composition was heated to 320F. until all the water of reaction had been evaporated and a drycomposition formed. The composition was then cooled to about 200 F.where phenyl a-naphthylamine was added as an oxidation inhibitor. Theremainder of the oil was added and the composition homogenized in aCharlotte mill.

The capric acid used above was a commercial acid obtained from coconutoil and having a saponification number of about 320.

The compositions prepared and their physical properties are summarizedin the following table.

EFFECT OF MOL RATIO OF ACETIC ACID TO INTERMEDIATE MOL. WT. ACID 30 A BC D E Formulation:

Glacial acetic acid, weight percent 4. 00 4. 00 4. 0O 4. 00 4. 00 Capricacid, weight percent... 1.19 1. 14 0. 92 0.76 0. 60 Hydrated lime,weight percent. 3.15 3. 10 2. 00 2. 70 2. 50 Phenyl A-naphthylamine,weizht percent 0.20 0. 20 0.20 0. 20 0. 20

Mineral libricating oil of 80 SSU at 210 F weight per- 320 320 320 320320 Mol Ratio of acetic a 4 caprie acid 6/1 10/1 12. 5/1 loll 19/1Properties:

Appearance Visc)sity SSU at 100 F- 1, 800 1, 603 1, 485 1, 492 1,431 Alnen test, weirhts carried-.. 6 6 7 4-ball Wear test, scar diam.

urn. (1,800 r.p.u1.-l0 kg.- 77 F.-1 hr) 0. 32 0. 29 0. 23 0. 24 0. 23Free alkalinity 0. 05 0.05 0.05 0.05 0- 05 a Centrifuge test:

4 r.-l,500 r.p.m., weight percent; solids 1.5 1.0 0.7 0.7 0.7 1 percentWaten. 20.0 10.0 2.0 2. 0 5.0 Sight glass life in days 2 10 35 35 1Commercial caprie acid derived from coconut oil and having asaponificetion number of about 320.

R Thixotro ic. 3 Excellent smooth fluid product.

The free alkalinity of Table II is in terms of NaOH.

The sight glass life test of Table II was carried out by passing thelubricant through the sight glass of a Manz ll lubricator containing a50/50 mixture of Water and glycerine at the rate of 1 quart per day.

The centrifuge test was carried out 'by simply centrifuging thelubricant sample and measuring the sediment. A second centrifuge wascarried out by mixing 1 wt. percent water with the lubricant and thencentrifugin Formulations A and B gave relatively more wear and were lessstable as measured by the centrifuge test, particularly in the presenceof water. This latter aspect is important because of the likelihood ofcontamination by condensation during storage. In addition, the sightglass life was poor. This also is important since nearly all marinediesel engines are lubricated by a forced feed system having sightglasses to regulate the lubricant flow. In many of these systems, thelubricant flows upward through a sight glass containing Water andglycerine. In this manner, the lubricant flow can be visually observedas the drops of lubricant pass upward through the waterglycerine mixtureand the fiow adjusted by a regulating valve. Since there is a sightglass for each cylinder, and

Ti considerable work is involved in cleaning a sight glass, the sightglass life of the lubricant is quite important. Thus, Formulation Awould require dismantling and cleaning the sight glasses every two days,while Formulations C, D, and E would operate 35 to 40 days withoutcleaning the sight glasses.

Formulations C, D, and E, which represent the invention, had betterextreme pressure properties, gave less wear, had better storagestability and good sight glass life as compared to Formulations A and B.These comparisons thus demonstrate the criticality of the molar ratio ofthe two types of acids in forming suitable lubricants.

What is claimed is:

1. A lubricant suitable for lubrication of upper cylinders of marinediesel engines comprising a major amount of mineral lubricating oil, andabout 5 to 12 Wt. percent dry calcium salts of acetic acid and C to Cstraight chain fatty acid-in a molar ratio of said acetic acid tosaidefatty acid of 11.521 to 25:1.

2. A method of lubricating the upper cylinders of marine diesel engineswhich comprises applying to the pistons of said engines the lubricant ofclaim 1.

3. A method of preparing the lubricant of claim 1 which corrprisesneutralizing said acids with lime in oil, followed by dehydration at atemperature of 250 to 350 F.

4. A lubricant according to claim 1, wherein the amount of thickener iswithin the range of 6 to 8 wt. percent and said molar ratio is about12.5 to 1 to 19 to 1.

5. A lubricant according to claim 1, wherein said O; to C acid isderived from coconut oil and has a saponification number of about 320.

References Cited in the file of this patent UNITED STATES PATENTS2,274,675 Earle Mar. 3, 1942 2,417,428 McLennan Mar. 18, 1947 2,606,753Holdstock Aug. 5, 1952 OTHER REFERENCES NLGI Spokesman, vol. 14, No. 12(March 1951), pp.

Can. I. Research, vol. 22, sec. B, pp. 7689, article by Gallay et al.

1. A LUBRICANT SUITABLE FOR LUBRICATION OF UPPER CYLINDERS OF MARINEDIESEL ENGINES COMPRISING A MAJOR AMOUNT OF MINERAL LUBRICATING OIL, ANDABOUT 5 TO 12 WT. PERCENT DRY CALCIUM SALTS OF ACETIC ACID AND C7 TO C10STRAIGHT CHAIN FATTY ACID IN A MOLAR RATIO OF SAID ACETIC ACID TO SAIDFATTY ACID OF 11.5:1 TO 25:1.